How do we create links?

I'm not sure how the link button is supposed to work. Typing a link in full doesn't work (this happens instead):
http://talk.planethunters.org/science/discussions/DPH10038fj
If I use the link button, this happens: [Your text to link here...](http://talk.planethunters.org/science/discussions/DPH10038fj "link test")

I'm not sure how the link button is supposed to work. Typing a link in full doesn't work (this happens instead):